The present invention relates to an information recording medium such as an optical disk or the like, an information recording and reproducing unit for using the information recording medium and a method for deciding a position of information when the information is to be recorded on the information recording medium.
As conventional techniques for reproducing fine signals of the size of at most a resolution limit in an optical disk unit and others, there are those techniques which are described in the Technical Digest of Optical Data Storage, 1991, Volume 1499, on pages 209 to 215 in the lecture number TUB-3 and on pages 216 to 225 in the lecture number TUB-4, for example. The feature of these techniques is that they use optical magnetic recording films of a plurality of layers in which layers for "masking" surrounding information are provided in addition to an information recording layer. Information (bits) recorded on the information recording layer appears at a portion where the temperature has risen by an irradiation of a reproduced light. Therefore, interference between adjacent bits is restricted even if the recording density has been increased, to thereby improve optical resolution.
According to the above-described prior art techniques, however, the information recording medium has been limited to an optical magnetic disk. Further, information which appeared on the "masking" layers remains even after reproducing spots have passed there. Accordingly, although it is possible to restrict the influence of bits before they are reproduced, the influence of the bits after they have been reproduced still remains within the adjacent bits. Furthermore, when information is recorded, a stronger beam is irradiated than when information is reproduced, so that it is not possible to efficiently record fine information bits.